It is known inter alia from U.S. Pat. No. 4,714,457 to utilize the plasma fraction in blood for the preparation of so-called tissue glue. According to the publication the coagulation factors, such as fibrinogen, fibronectin, factor VIII, and factor XIII are precipitated from the plasma fraction. These coagulation factors are precipitated for instance by cryoprecipitation or by means of a precipitation-promoting agent such as ethanol. The precipitated precipitate includes mainly fibrinogen and is used as tissue glue, such as in connection with operation wounds, by the addition of a suitable enzyme, such as thrombin. Like in nature, the fibrinogen and thrombin form together fibrin, which is an insoluble network of fibre-like material constituting a kind of tissue glue interconnecting the wound surfaces during a healing process. On account of the latter effect, a concentrate of coagulation factors containing mainly fibrinogen turned out to possess a favourable effect on the healing process after an operation. For short, the concentrate of coagulation factors is below referred to as fibrinogen, as said fibrinogen is the main ingredient thereof.
Several methods are today used for separating plasma from blood. The separating process can be performed by means of filters or centrifuging techniques or by way of combinations thereof. The methods are usually known as "plasmapheresis". The methods have been developed because it is often sufficient to give the patients a plasma transfusion, whereby it is unnecessary also to remove slowly regenerating blood cells from the donor.
The precipitation of fibrinogen from plasma has previously been performed in closed bag systems. The precipitation into such bags (blood bags) necessitated production of particular means for securing the bags in a centrifugal bowl, in which the centrifuging is to be performed. In addition, it is difficult to separate the fibrinogen from the plasma in a reliable manner. The flexibility of the blood bags often results in the viscous fibrinogen loosening from the bag and mixing with the remaining plasma in the bag, whereby the concentration is substantially reduced. The latter problems have had the effect that these methods are not used by way of routine today.